Pressure-sensitive adhesive tape



tented $ept. 13, 1949 PRESSURE-SENSITIVE ADHESIVE TAPE Paul F. Ziegler,Winnetka, Ill., assignor to The Kendall Company, Boston, Mass, 9.corporation of Massachusetts No Drawing. Original application December10,

1943, Serial No. 513,711.

Divided and this application August 20, 1948, Serial N0. 45,440

4 Claims. (Cl. 117-122) This invention relates to pressure-sensitiveadhesive tapes, and more particularly to the preparation of such tapeswherein the adhesive thereof comprises a polyvinyl pressure-sensitiveadhesive, and wherein the backing may be a transparent, non-fibroussheet material'such as regenerated cellulose.

An accepted backing material for transparent pressure-sensitive adhesivetapes is regenerated cellulose. Because of its smooth, non-fibrous,glossy surface, commercially satisfactory regenerated cellulose adhesivetapes have included a priming coat for the purpose of improving the bondbetween the pressure-sensitive adhesive and the backing by creatin apreferential afiinity of the adhesive for the surface of the primedbacking to which it is applied, compared with its affinity for thesurface of the backing without the interposition of the priming coat,and thus permit, after the tape has been wound upon itself in roll form,successful unrolling thereof without destructive separation ordelamination of the adhesive from the backing. Rubber-resin adhesivesgenerally used as pressure-sensitive adhesives in such tapes do not havecommercially sumcient adhesion, when applied directly to the smoothglossy surface of regenerated cellulose in the absence of a priming coator of some special technique of application, to permit such satisfactoryunrolling.

This application is concerned with the preparation of non-rubberpolyvinyl resin pressuresensitive adhesives which may be directly amxedas firmly adherent coatings to regenerated cellulose or other similarsmooth-surfaced transparent sheet backlngs and is a continuation-ln-partof my application Serial No. 349,973, filed August 2, 1940, now PatentNo. 2,426,257, and is a division of my prior application Serial No.513,711 filed December 10, 1943.

The foregoing application discloses inter alia the preparation ofpressure-sensitive adhesives formed of a polyvinyl ester, a resincompatible with the polyvinyl ester, and a non-volatile liquidplasticizer compatible with both the polyvinyl ester and the resin;wherein the polyvinyl ester serves as the film-formin vehicle for theadhesive and is present in sufficient proportion to impart structuralsupporting characteristics which permit the formation of a relativelythin continuous cohesive flexible coating thereof on a flexible sheetbacking, inclusive of regenerated cellulose, to form apressure-sensitive adhesive tape.

2 backings are concerned, such an adhesive has been found to have aremarkable afiinity for the regenerated cellulose surface to which ithas been applied when the adhesive is prepared in accordance with thefollowing formula:

Santicizer B16 (butyl phthalyl butyl glycollate) 42 The vinyl co-polymeris a standard polyvinyl resin of the acetate-chloride type and in theform which has been used for the adhesives hereof has a chloride contentof about 87% and a molecular weight of about 9,50010,500. It is aproduct of Carbide 8; Carbon Chemicals Corporation. It constitutes thefilm-forming vehicle and is responsible for the elastic and cohesivecharacter istics of the adhesive.

The Nevillac resin is a phenol-modified coumarone-indene resin,- aproduct of Neville Company, and as used in the above formula, has amelting point in about the range of to C. It forms the adhesiveconstituent of the adhesive.

Santicizer B16 is one of the Monsanto Chemical Companys non-volatileliquid plasticizers which are alkyl phthalyl alkyl glycollates. Thisparticular Santicizer B16 is butyl phthalyl butyl glycollate. Itactivates the Nevillac resin to sticklness and renders the adhesivecoatin as a whole flexible.

These three ingredients may be added to a common organic solvent, suchas ethyl acetate or acetone, in the order of plasticizer, co-polymer andNevillac. The solvent can then be driven off as necessary to a pointwhere the solidscontent is suitable for spreading as by a doctor bladeor roll on regenerated cellulose sheet material, for example to about 50to 80%, preferably 75%. Both the mixing and spreading may beaccomplished at room temperature, but artificial drying may be helpfulin driving off the solvents after the solution is spread upon thebacking. It has been found that the tack of the coating improves as thethickness increases from .002" to .005". Hence the thicker coat isdesirable.

A regenerated cellulose sheet, thus directly coated with my transparentadhesive in a onecoat operation without any interposed primer coat, maybe slit and rolled and will meet the commercial requirements for atransparent cellophane pressure-sensitive adhesive tape. The

In so far as tapes having regenerated cellulose 55 roll may be unwoundwithout delamination of the adhesive onto the backing even in theabsence of separate interliners, and the tape can, like the usualcellophane tapes, be re-used. The adhesive, which is clear andtransparent, ages well and has good adhesion to metal, wood, paper andother materials to which cellophane tapes are now generally applied. Theadhesion to skin is, however,-

not as aggressive as that of rubber-resin pressure-sensitive adhesives.This particular quality has been found to be a decided advantage becausethe tape is thus less sticky and less annoying to handle.

The proportions and ingredients so far recited represent the bestformula with Hard Nevillac resin (1. e. 85-95 C. melting point) forgeneral regenerated cellulose use. It should be noted that thefilm-forming ingredient and adhesive resin constituent are in a 1 to 1ratio. Variation of this ratio is permissible, but experience shows thatvariation has resulted in sacrifice in quality, particularly with regardto the affinity for the regenerated cellulose. A decrease in vinylpolymer content, so that the ratio is 20-40-42, instead of 30-3042, willresult in a decrease in the adhesion and cohesion characteristics, butwill increase the track. on the other hand, if the plasticizer contentbe independently varied within the limits of from 90 to 50% of thecombined vinyl polymer-resin base, the adhesion and cohesion willincrease with decrease of plasticizer content, but the tack willdecrease. In our experience, the l to 1 ratio provides the mostdesirable qualities of adhesion and cohesion for the purposes of aregenerated cellulose tape, and the tack can be kept suitably high withthis ratio by the use of a higher proportion, e. g., 70% of plasticizer,aided, if desired, by a coating thickness of about .005". In any event,the film-forming vehicle content must be sufliciently high to giveadequate cohesive strength to the adhesive coat, and, in accordance withthis invention, must exceed 12% of the total content.

Equally successful results have been secured with the use of softerNevillac resins, which range down to a melting point of about 65 C.These softer resins are also phenol modified coumaroneindene resins. Useof such softer resin permits a reduction in the plasticizer content,and, from the standpoint of cost and lighter color, an adhesive havingthe following formula is even more desirable than one following the HardNevillac formula:

Parts Vinyl co-polymer VYHH 30 Soft Nevillac resin 30 Santicizer B16(butyl phthalyl butyl glycollate 36 It will be noted that here theplasticizer content is in the ratio of .6 to the combined vinylcopolymer and Nevillac content. Generally this plasticizer ratio may be.1 part less (figured on the combined co-polymer resin content) than inthe case of the Hard Nevillac formula where, as above given, the ratiois .7. However, additional plasticizer variation will producecorresponding variation in tack, adhesion and. cohesion results,generally corresponding to those heretofore discussed in the case of theHard Nevillac.

In tapes constructed in accordance with this invention the adhesion ofthe tape mass to other regenerated cellulose surfaces may be in therange of from 0.6 to 1.2 or more pounds and the mass coating exhibitssubstantially the same degree of adhesion to its regenerated cellulosebacking 4 as it does to an external regenerated cellulose surface.

For the purposes of determinin "adhesion to external surfaces, asreferred to in the preceding paragraph, a one-inch wide strip ofconvenient length of the tape to be tested is placed tacky' surface downupon a smooth surfaced Bakelite panel under temperature conditions of 70F. The panel is then placed at a 15 inclined position and a seven-poundroller which is free to move vertically is passed over the strip at therate of one foot per minute up and back to adhere the pressure-sensitivesurface to the panel. One end of the strip is then attached to the clampof a tensile strength Scott tester and the average number of poundsrequired to pull a substantial length of the tape ofi the Bakelitesurface at an approximate 180 angle and at a rate of one foot per minuteis determined.

For the purposes of determining adhesion of a coating to its ownbacking, a double-face adhesive strip is interposed between the Bakelitepanel and the strip to be tested. Such a doubleface adhesive tape may bean ordinary surgical tape coated on both sides. The regeneratedcellulose tape to be tested is then separated at one end of the tapefrom the adhesive mass and the clamp of the tester is afllxed to thisbacking alone, the tester stripping the regenerated cellulose backingfrom its own mass which remains adherent to the double-face tape.

In addition to adhesion characteristics of the above type, it has beenfound that the mass film has extensive stretchability and a tensilestrength in a one-inch width of about pounds at 70 F. These lattercharacteristics, taken in connection with the adhesion characteristics,are factors contributing to the production of a tape which does notdelaminate upon unrolling.

Cohesion of the above referred to masses are shown to be such that theyhave a "creep characteristic exceeding 20 minutes as determined byplacing a one-inch strip of the tape of several inches length, tackyside down, over a horizontally disposed, raised, one-inch diameterBakelite cylinder, and suspending a one-pound weight from each end ofthe tape. The apparatus is then placed in an oven at 105 F. for a periodof 15 minutes, after which time the tape is slashed across the top ofthe cylinder and the time required for either portion of the tape tofall from the cylinder is an arbitrary value assigned to the tape as itscreep value. Some tapes of this invention reach a creep value exceedingminutes.

A further determinative characteristic of adhesive tapes is that ofaging. Tapes of this invention have successfully withstood a standardaccelerated aging test comprising storage of the tape under 300 lbs.oxygen pressure at F. for a period of one week. After such storage thetapes are still tacky and having adhesion values, determined inaccordance with the previously given test, in excess of 0.6 lb., theycan still be unrolled without delamination and instances of similarbehavior have occurred even when the period in the oxygen bomb is asmuch as 3 weeks.

A further desirable feature is found in these tapes in that they exhibita definite stability over a range of temperature and can be unwoundwithout any detrimental delamination of the adhesive at any temperaturein ranges as wide as from 40 to F.

The Monsanto Chemical Company produces Santollte resins which may besuccessfully used instead of Nevillac resins. These Santolite resins arearyl Santolite MHP, preferred because of its light color, has a meltingpoint of about 65 C. and therefore its action is more similar to that ofthe soft Nevillac resin and should be used in the proportion of the softNevillac resin. Santolite MS, being a still softer resin (meltingpoint=50 C.) detracts somewhat from the cohesion and requires a stillfurther reduction in plasticizer with the plasticizer content, in somecases, being as low as 30% of the combined co-polymer resin content.However, it is contemplated that adhesives of this invention may beapplied to suitable backings by a calendering operation rather than by asolvent spread as hereinbefore described. Thus the ingredients may bemixed and brought to the proper consistency for spreading bytransferring the mix to a hot rubber mill to dissolve the solvent; or insome cases of relatively high resin-plasticizer content (for instance, 2parts of co-polymer to 3 parts of resin and 3 parts of plasticizer) thecopolymer may be dissolved directly in a hot (140- 150 C.) mixture ofthe resin and plasticizer and calendered at that or a lower temperature.

With regard to the film-forming vehicle, the superior resultsaccomplished on cellophane with the co-polymer have not been attainedwith other polyvinyl esters, although polyvinyl acetate will be foundacceptable especially when a smoothsurfaced backing is not contemplatedor when priming coats are permissible. In general, polyvinyl acetate hassofter characteristics than that of the co-polymer and therefore impartsless cohesive strength to an adhesive, while polyvinyl chloride haslimited solubilities, a characteristic which renders solvent operationsdiflicult.

In the case of polyvinyl acetate, pure phenolic resins (Beckacite) maybe satisfactorily used as well as Nevillac. The Beckacite resins are notcompatible with the co-polymer.

As to the plasticizer, modifications can be made so long ascompatibility in the proportions used is observed. Other satisfactoryplasticizers for the Nevillac-co-polymer mix, though not preferred, areother non-volatile liquid esters of phthalic acid, including either thedialkyl phthalates-dibutyl phthalate and dicapryl phthalateor othermixed esters of phthalic acid and alcohols or hydroxy acids, dibutylsebacate and mixed aryl sulfonamides, such as Santicizer 8 (MonsantoChemical Co.) Either dibutyl phthalate or Santicizer B16 are compatiblewith polyvinyl acetate-phenolic resin mixes.

Adhesives may be suitably formulated in accordance with this inventionfor application to other sheet backings, either of the non-fibrous orfibrous variety, including woven or unwoven fibrous backings and smoothsurfaced backings of the type of cellulose acetate, ethyl cellulose,polyvinyl ether, rubber hydrochloride or polyamides such as sheet nylon.

sulphonamide-formaldehyde resins.

I claim:

1. A pressure-sensitive adhesive tape comprising a. flexiblesmooth-surfaced non-fibrous sheet backing material having aflixeddirectly thereto on one side a firmly adherent coating of a normallytacky pressure-sensitive adhesive, whereby said tape may be rolled uponitself and um'olled without destructive delamination of the tape, saidadhesive consisting essentially of a polyvinyl acetate-chlorideco-polymer film-forming vehicle and a compatible normally solid arylsulphon amide-formaldehyde resin in about equal proportions, and anon-volatile liquid alkyl phthalyl alkyl glycollate plasticizercompatible with both said co-polymer and said resin in the proportion ofabout 30-90% of the combined weight of said copolymer and resin.

2. A pressure-sensitive adhesive tape comprising a flexiblesmooth-surfaced non-fibrous sheet backing material having aflixeddirectly thereto on one side a coating of a normally tackypressure-sensitive adhesive, said adhesive being formed of a polyvinylacetate-chloride co-polymer film-forming vehicle, arylsulphonamide-formaldehyde resin and a non-volatile liquid alkyl phthalylalkyl glycollate plasticizer compatible with both said polymer and saidresin, the proportion of ingredients being about 20-30 parts ofco-polymer, about 30-40 parts resin and about 36-42 parts plasticizer.

3. A pressure-sensitive tape as claimed in claim 2 wherein theplasticizer is butyl phthalyl butyl glycollate.

4. A pressure-sensitive adhesive tape comprising a flexiblesmooth-surfaced non-fibrous sheet backing material having aflixeddirectly thereto on one side a firmly adherent coating of a normallytacky pressure-sensitive adhesive, whereby said tape may be rolled uponitself and unrolled without destructive delamination of the tape, saidadhesive consisting essentially of a polyvinyl acetate-chlorideco-polymer film-forming vehicle and a compatible normally solid arylsulphonamide-formaldehyde resin having a melting point from ESQ- C.,said co-polymer and said resin being in about equal proportions, and anonvolatile liquid plasticizer compatible with both said co-polymer andsaid resin in the proportion of about 30-90% of the combined co-polymerresin weight.

PAUL F. ZIEGIER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

